The genes coding for DNA ligase have been isolated from E. coli as a molecular hybrid with bacteriophage lambda gt DNA. Also, the genes coding to DNA polymerase I from both Klebsiella pneumoniae and Klebsiella aerogenes have been isolated. Work is in progress to construct by genetic and biochemical techniques a new hybrid gamma gt phage, which upon induction will greatly overproduce these gene products. A plaque RNA hybridization technique has been developed by which one can screen for a hybrid lambda gt phage that contains homologous DNA. Using this technique we are presently screening for a number of lambda gt's containing specific genes from yeast. Bibliographic references: "An Electron Microscopic Method for Studying and Mapping the Region of Weak Sequence Homology Between Simian Virus 40 and Polyoma DNAs." "T Antigen Binds to Simian Virus 40 DNA at the Origin of Replication." Reed S.I., Ferguson, J., Davis, R.W., and Stark, G.R., Proc. Nat. Acad. Sci. USA 72, 1605-1609 (1975).